Quantum Radars Could Unstealth the F-22, F-35 and J-20 (Or Not)

In April 2018 it was reported that the Canadian Department of National Defense was investing $2.7 million in research at the University of Waterloo to investigate quantum radar technology. This brings Canada into a technological race in which China apparently has taken the lead.

Though far from being a mature technology, quantum radar might eventually provide a capable means of detecting stealth fighters and bypassing electronic warfare capabilities. While Canada has opted out from acquiring F-35 stealth fighters, the North American Aerospace Defense Command (NORAD) operates jointly with the United States and must contend with potential intrusions by new Chinese and Russian stealth aircraft.

Quantum weapons technology may seem to belong more to the realm of Star Trek than a real-world weapon system. However, the tech is real, leveraging the principle of “quantum entanglement.” This is a phenomenon in which conditions affecting one subatomic particle also manifest themselves on an ‘entangled’ partner particle—even, rather uncannily, when they are far apart.

A quantum radar functions by using a crystal to split a photon into two entangled photons. (Reportedly, finding a “fast, on-demand source of entangled photons” is the technical hurdle Canadian researchers are focusing on.) Then the radar beams one half of the entangled pair outwards, and monitors the corresponding effects on their entangled partners. If the beamed particles bump into, say, a stealth fighter, the effecton the beamed photon would be visible on the un-beamed partner photon as well. Then the photons which register a ‘ping’ are sorted out from the unaffected photons to form a sort of radar image.

This radar-like capability would not be susceptible to many of the technique designed to circumvent radio wave reflection—ie, a reduced radar cross section and radar-absorbent materials—and also would not be affected by jamming and other electronic warfare ploys, which play an important role in defeating air defense radars.

Furthermore, the entangled photons would not be detectable—giving detected targets little warning—and would not be traceable back to their source. This means that, unlike a traditional air defense radar, which exposes itself to detection whenever it actively emits radio waves to search for aircraft, a quantum radar does not broadcast its presence and make itself vulnerable to anti-radiation missiles.

However, quantum radars have their limitations; like traditional radars, they degrade in resolution over longer distances. This is because the entangled particles do eventually lose the coherence of their quantum state over long distances, a phenomenon which can worsen in adverse weather.

In September 2016, China claimed its China Electronic Technology Group Corporation (CETC) had developed a working quantum radar with a range of 100 kilometers (sixty-two miles). This was reportedly achieved through the development of highly efficient single-photon detectors (this article has a more detailed technical explanation). It’s worth noting that many commentators are skeptical that the Chinese quantum radar is close to being usable under nonlaboratory conditions.